Cyro EM, in conjunction with X-ray crystallographic data and antibody labelling, has been very effective in addressing biological structure-function issues in viruses. The IVEM has the potential for decreased radiation damage, higher resolution, and also serves as a comparative base for contrast-tranfser function deconvolution. Several types of large viruses are being imaged, both tilted and untilted, by cryo-EM. In addition, plastic-section tomography is being conducted to study membrane interactions during virus budding. This is an ongoing project.